1. Field of the Invention
The present invention relates to a seat sensor used for detecting that an occupant is seated on a vehicle seat and in particular, to a seat sensor including a sensor cell which becomes electrically conductive when the sensor cell is applied with a load of the occupant and so on.
2. Description of Related Art
JP10-39045A discloses a seat sensor, which is arranged in a seat face portion of a vehicle seat and is provided with plural sensor cells all connected in parallel. In this seat sensor, when one of the sensor cells turns on (becomes electrically conductive), it is determined that an occupant seats himself or herself (i.e., the occupant is seated) on the vehicle seat.
In this case, however, even when a baggage is placed on the vehicle seat, it may be erroneously detected that the occupant seats himself or herself on a vehicle seat because any of the sensor cells possibly turns on.
Therefore, JP2005-153556 corresponding to US No. 2005/0140210 discloses a seat sensor for solving this problem. This seat sensor is arranged in a seat face portion of a vehicle seat and is provided with two sensor cells which are arranged in a vehicle front side of the seat face portion and are connected in series with each other, and two sensor cells which are in a vehicle rear side of the seat face portion and are connected in series with each other. The two sensor cells arranged in the vehicle front side and the two sensor cells arranged in the vehicle rear side are connected in parallel with each other. According to the seat sensor, only when at least the two sensor cells arranged in the vehicle front side or the vehicle rear side turn on simultaneously, it is determined that the occupant seats himself or herself on the vehicle seat.
A baggage placed on a vehicle seat, for example, a handbag has an extremely small mass as compared to that of an occupant. Therefore, if the baggage is placed so that a force is exerted equally on a seat face portion of the vehicle seat, there is a slight possibility that a sensor cell turns on. However, if a baggage is placed in such a manner as to lean on a seat back rest portion of the vehicle seat, the baggage results in standing on its corner, possibly causing a large load to be applied on a specific position of the seat face portion. For example, there is a case where a large load is applied on the vehicle rear side of the seat face portion. In such a case, since the two sensor cells in the vehicle rear side simultaneously turn on even in the seat sensor disclosed in JP2005-153556A corresponding to US No. 2005/0140210, an erroneous detection due to the baggage possibly occurs.